Knee brace devices are designed to provide control over movement of the human knee following injury, during recuperation from injury, and to provide protection of the knee to prevent, treat, or aid in the healing of, knee injury or disease. Existing orthopedic knee braces do not take into account a complete understanding of the anatomy of the knee joint and particularly knee kinematics. For these reasons, existing knee braces fail to accommodate and adequately control a full range of motion of the knee. These deficiencies in existing knee brace devices limit their usefulness and impair the ability of the knee joint to heal during recuperation following injury or disease.
The human knee joint is formed by the distal end of the femur, particularly the medial and lateral femoral condyles, and the proximal end of the tibia, particularly the respective medial and lateral tibial plateaus. The condyles of the femur articulate upon the tibial plateaus. The medial and lateral condyles are not symmetric in size or shape, with respect to one another, nor are the articular surfaces of the corresponding tibial plateaus.
The knee joint is a complex hinge mechanism with many motions in multiple planes taking place simultaneously, with six degrees of freedom. Flexion and extension take place in the sagittal plane. During normal human locomotion the knee ranges from zero degrees, which is defined as full extension (straight leg), to an average of about 60 degrees of flexion (bent knee position). When a person increases activity, for example jogging or sprinting, knee range of motion increases somewhat relative to the person's velocity. The natural roll and glide of the femur on the tibial plateau occurs in an anterior and posterior motion within the sagittal plane. As the femur rolls back on the tibia during flexion it also glides. Since the medial and lateral condyles are essentially spherical and have different radii, they rotate and glide at a different rate. The differential rollback creates a complex asymmetric motion to the knee.
Further motion linked to the knee flexion and extension occurs in the frontal plane. As the knee flexes, the ankle moves toward the midline of the body to create adduction (or varus). As the knee extends, the ankle moves away from the midline of the body to create abduction (or valgus). Simultaneous motion also occurs in the transverse plane. The tibia exhibits internal and external rotation with respect to the femur. As the knee flexes the tibia internally rotates with respect to the femur. As the knee extends the tibia externally rotates. This phenomenon is known as “the screw home mechanism.” The screw home motion is a result of ligament and other soft tissue tension, as well as the articular geometry and relationship between the medial and lateral femoral condyles with the respective tibial plateaus. As the knee flexes and extends, the tibia further exhibits proximal/distal motion and medial/lateral motion with respect to the femur.
Injury to the knee, such as major ligament injury, is a major factor leading to knee osteoarthritis or degenerative joint disease. Injury to the knee disrupts the dynamic coupling of the various independent but simultaneous motions. Interference with the natural anatomical motions of the knee results in incongruence between the femoral condyles and their respective tibial plateaus. This incongruence creates instability of the knee as well as excessive loading of the articular surfaces of the joint, leading to knee osteoarthritis.
The knee is the most commonly affected weight-bearing joint, and varus deformity is a common malalignment of the knee associated with osteoarthritis. Nonoperative measures that have been shown to be effective for the treatment of osteoarthritis of the knee include, education, telephone contact, weight loss, a walking program, a muscle-strengthening program, and analgesics to control pain. Intra-articular injections of hyaluronic acid, orgotein, and glucocorticosteroids seem to provide short-term relief, but they must be repeated frequently.
There are a number of systemic factors which increase vulnerability to joint damage, most notably age (esp. female gender after age 50), genetic susceptibility and obesity. A variety of other systemic factors, such as nutrition and physical activity, also play a large role. Those systemic factors that increase systemic vulnerability to joint damage either work by or contribute to intrinsic joint vulnerability.
Local factors and the local joint organ environment are anatomic and physiologic aspects of articular and periarticular tissues, especially emphasizing those elements that influence load distribution. These factors are specific to the joint site. The local environment tends to be neglected in current therapy, except exercise, and is a relatively untapped target for disease modification. Improving the local environment may alter the course of the disease. At minimum, it can strengthen the effect of pharmacologic agents.
In normal knees, biomechanical forces create an adduction moment during stance which results in 60 to 80 percent of the load going to the medial compartment. This biomechanical phenomenon may explain the greater frequency of medial versus lateral tibial femoral osteoarthritis. The adduction moment increases with the increasing magnitude of varus alignment, which contributes to medial osteoarthritis progression. Thus, varus alignment increases the adduction moment, which in turn increases medial knee compartment load. Conservative approaches that unload the compartments stressed by malalignment include bracing and wedge insole foot orthoses.
Orthopedic devices that have been evaluated for the treatment of varus gonarthrosis include wedged insoles and braces. Two main types of braces, sleeves and unloading braces, are available. Each is used in an attempt to decrease loads through the tibiofemoral joint. As the sleeve provides little mechanical support to the knee, it is thought that the feelings of improved stability and reduced pain are largely due to an improvement in joint proprioception. Kirkley, et al., J. Bone and Joint Surgery, 81: 539–547, 1999.
Osteoarthritis is a common disorder affecting synovial joints, with structural changes of osteoarthritis present in approximately half of the adult population. Osteoarthritis of the knee often results from joint overuse and or joint injury leading to premature breakdown of articular and lunar cartilage within the femoral-tibial compartment of the knee. Roughly seven million people are currently diagnosed with knee osteoarthritis, and this number is expected to double by the year 2020. It is expected that 18 percent of the U.S. population will have some form of arthritis and commensurate increase in costs for their care by the year 2020. Osteoarthritis knee braces attempt to create an opposing abduction moment (in the case of varus knee osteoarthritis), to unload the diseased compartment of the knee. Although there are numerous knee braces commercially available. For example, the Unloader® (Generation II USA) has been tested in randomized clinical trials and proven effective. The Unloader® brace works by creating a force which reduces the load on the symptomatic compartment by a three-point force system and a single upright hinge. The angle of the hinge is adjustable, and increases the abduction moment, to further decrease the load to the medial compartment. A ‘dynamic force strap’ produces the contralateral third point of force. See Knee Osteoarthritis: A Biomechanical Approach to the Pathogenesis and Treatment, Clinical Symposium at the American College of Rheumatology (ACR) and the Association of Rheumatology Health Professionals (ARHP) Annual Scientific Meeting, Nov. 11–15, 2001 in San Francisco, Calif.
Knee braces have been designed to protect and provide control for the human knee. Most designs ignore the three dimensional asymmetric motion critical to the healthy preservation of the anatomical knee joint, controlling motion in a single, sagittal plane. The rigidity found in these types of braces provides good protection from external impact to the knee, but as a result of the limited single plane motion, do not protect or preserve the articular surfaces of the joint.
Examples of previously described knee braces include devices for stabilizing a knee joint that provide a hinge mechanism with a cam follower and a cam slot. U.S. Pat. No. 4,723,539. The hinge allows the knee joint to move in a forward to rearward motion only within the sagittal plane during flexion and extension of the knee joint while in the appliance. The hinge mechanism of the knee brace does not control any other planes of motion of the knee joint.
Other known knee brace devices provide a hinge for use in an orthopedic knee brace, wherein the hinge has linking and pivot members proposed to simulate movement of the tibia in relation to the femur. U.S. Pat. No. 5,230,697. In this type of hinge mechanism, the pivot point in the hinge varies or changes during rotational movement. Principal movement of the knee within the knee brace occurs within the sagittal plane. The hinge mechanism reportedly controls movement within a single plane, but fails to control other planes of motion of the knee joint.
Other examples of hinges for use in an orthopedic knee brace attempt to provide for movement of the knee joint in three dimensions. These knee braces may allow movement in four of the six degrees of freedom, and potentially five of the six degrees of rotational freedom, of the anatomical knee joint. U.S. Pat. No. 5,792,086 and U.S. Pat. No. 5,107,824. However, in the first of these designs the proximal distal motion of the tibia in relation to the femur is accommodated by a sliding portion of the tibial section of the knee brace, not by the hinge mechanism. The sliding portion adds considerable bulk to the knee brace, which may be undesirable to certain wearers of knee orthoses. Another limitation of this design is that the hinges and the entire knee brace are flexible, not rigid. The plasticity of all components is necessary to prevent binding and restriction during asymmetric motion of the hinges. When hinges with three dimensional geometry in a pin-in-slot pattern of the prior design are used in a rigid knee brace, the prior art knee brace tends to bind resulting in excessive component wear.
The knee braces of prior design may fail under certain conditions of use. The knee braces of prior design do not offer protection to the wearer's knee and leg from outside impact. The knee braces of the prior design may fail under load. The slot and pins may wear substantially due to friction, placing a burden on the knee brace and the wearer, and limiting the useful life of the product.
In the second design, the knee brace may lack the rigidity necessary to properly brace the knee joint under certain conditions. In one important aspect, the hinges of the knee brace are not rigidly fixed relative to one another. The medial and lateral hinges exist independently in medial and lateral cuffs, respectively, and are held together by flexible straps. This flexibility allows movement of the hinges and or the thigh and calf cuffs to prevent the binding that takes place as a result of the mechanical hinge asymmetry. This knee brace therefore does not brace the knee joint in six degrees of freedom of movement.
Additional knee braces are provided in a variety of design variations and are known in the art as produced by such makers as Omni™, Donjoy™, Orthotech™, BREG™, Lenox Hill™, Townsend™, and CTI™. Each of these alternative knee brace designs has notable deficiencies in accordance with one or more aspects of the foregoing discussion. None of these additional devices properly brace the knee joint in six degrees of freedom of movement.
In view of the foregoing, a compelling need exists in the art for an orthopedic knee brace that will more accurately track anatomical motion of the knee and provide an improved construction as required for sufficient external support and protection of the knee. A related need exists for an improved knee brace adapted to treat or prevent advancing symptoms of osteoarthritis of the knee.